This invention pertains to the field of fluid mixing systems and more particularly, to induction nozzles associated with air circulation systems.
Induction mixing nozzles are frequently employed in air circulation systems. Generally, an induced secondary flow of ambient room air is mixed with a primary flow of supply air. Of course, the primary air temperature may be above the ambient air temperature for a heating system, and the primary air temperature may be below in an air conditioning (cooling) system. Alternatively, such air circulation systems may control humidity or some combination of temperature and humidity. Using induction mixing nozzles, the amount of duct work and insulation used in the system can be kept to a minimum and a sufficient mass flow rate of circulated air can be achieved without the necessity of injecting air flow directly into the room at high velocity or at extreme temperatures or humidity. The flow rate through the mixing nozzle is usually thermostatically controlled so that the ambient air temperature within the room can be maintained at a selected level. Pressure independent, constant flow rate valves of the type shown is U.S. Pat. No. 3,204,664 issued to Dimiter Gorchev, et al on Sept. 7, 1965, may be employed in such systems to automatically maintain a selected flow rate without the use of refined feedback controls.
In a typical prior art induction mixing apparatus, the secondary flow induction port surrounds a standard venturi nozzle. In this type of nozzle, the flow exits through a circular orifice, filling the entire plane of the oriface. In these devices, the ratio of the rates of induced secondary flow to primary flow is directly related to the primary flow rate. As a result, the composite flow rate decreases as the primary flow rate decreases. Thus, for example, in a heating system, as the room (ambient) temperature approaches a desired value, the flow rate of primary air (at high temperature) is reduced, thereby reducing the secondary and composity air flow rates. This dependence of the composite air flow rate upon the temperature differential between the secondary (ambient) and primary air leads to conditions where air circulation within a room might virtually cease.
A more complex type of induction nozzle is illustrated in U.S. Pat. No. 3,638,679, issued on Feb. 1, 1972 to Dimiter Gorchev. In that nozzle, the flow rate of the induced air is controlled by an adjustable valve and mechanical linkage so that the induced air enters a mixing nozzle at a rate that is inversely related to the flow rate of the primary air. As a result, a relatively constant flow rate, variable temperature output air flow may be provided by that mixing nozzle. However, the adjustable valve and mechanical linkage utilized by such induction nozzles form a complex mechanical arrangement which is correspondingly expensive to produce with tolerances which permit commercially acceptable temperature control, air flow and system reliability.
A further disadvantage to the prior art systems, is the high frequency noise generated by wave disturbances in the regions of the primary and secondary fluid ports.
Accordingly, it is an object of this invention to provide a relatively constant output flow rate induction nozzle for use in air circulation systems.
A further object is to provide an induction nozzle by which the temperature of the output mixture may be controlled by the primary fluid flow rate while the composite output flow rate is maintained relatively constant. A thermostat control associated with such a nozzle could respond to changes in room temperature by automatically selecting the optimum primary air flow rate since the temperature of the air entering the room through the mixing nozzle is always known.
Still another object is to provide a relatively low noise induction nozzle for use in air circulation systems.